To achieve efficient chemical processing, it is necessary to precisely control a number of processing parameters, such as temperature, pressure, mixing conditions, exposure of reactants to catalyst material, exposure of reactants to products and/or byproducts and exposure of reactants to actinic radiation. Certain chemical reactions are particularly difficult to perform in an optimal manner because the chemical reactions occur very quickly, sometimes before the reactants are completely mixed together. Certain non-stoichiometric portions of the partially mixed reactants may cause reaction products other than those desired to be produced.
Conventional chemical processing equipment typically holds a relatively large volume of materials and consequently has a relatively large volume to surface area ratio, and are thus particularly ill-suited for high speed chemical reactions. Different portions of the reactant materials contained within such processing equipment are more likely to be exposed to different histories of conditions. In the case of a conventional tank reactor, for example, when reactants are introduced they are typically added in separate streams, usually at controlled rates, and are then mixed together. The so-called T-mixer has been used to mix incoming streams together before they enter a reactor tank. For chemical reactions that occur rapidly, i.e., typically in less than one second, insufficient mixing may have occurred, even with use of the T-mixer, before the reaction is well established. Portions of the incompletely mixed mixture may be starved of one or the other reactant and undesired secondary reactions may occur which produce undesired byproducts.
Rapid stirring of the reactants may reduce this mixing history difference, but will not eliminate it. As a result of the nonhomogeneous mixing history, different portions of the reactants may chemically react differently. Undesired reactions may occur in portions of the reactants that cause localized heating in these different portions. This localized heating may accelerate undesired reactions. This may result in the production of undesired waste products, which may be hazardous and/or which must be properly disposed of. In extreme situations, reaction rates may accelerate to uncontrollable levels, which may cause safety hazards, such as potential explosions.
If, however, the volume in each reactant stream being mixed is substantially reduced, then the speed of mixing of the reactants may be greatly increased to substantially improve the control of homogeneity of mixing history of the reactants.
It has been recognized that a high degree of flow turbulence enhances the ability to rapidly mix two or more reactants together. Rapid mixing is known to be important for rapid chemical reactions. A high degree of turbulence is also known to enhance heat transfer as well as mixing rates. Thus a structure having both a low contained volume and a high degree of flow turbulence is particularly advantageous for precise control of high-speed chemical reactions.
Mixer assemblies having highly turbulent flow have been constructed by machining the desired passages and chambers in metal plates, using conventional metalworking techniques, and then assembling the plates into a stack and either clamping the stack together or permanently joining the stack, as by welding or soldering. An example is U.S. Pat. No. 3,701,619. Structures formed using conventional machine tool techniques cannot economically achieve volume to surface area ratios that are very low. The materials of construction of conventional chemical processing apparatus, such as steel and specialty iron alloys, furthermore may be subject to corrosion and wear, may have undesirable effects on catalytic activity, or may "poison" a catalyst.
It is an object of the present invention to provide a chemical processing unit that mixes reactants in a rapid and efficient manner, such that chemical reactions are not limited by mass transfer considerations. The present invention provides the capability to integrate one or more mixing/reaction units with control elements into a larger integrated chemical processing system to meet the needs of a specific high-speed chemical reaction. A feature of the present invention is that it can be economically used in the laboratory, to make a range of precise sizes of mixing/reaction units, to perform the basic chemical reactions for determining the optimum operating parameters. Commercial production volumes may then be readily achieved by replicating the mixing/reaction units and operating them in parallel in a larger integrated chemical processing system.
Advantages of the present invention, when used in a larger integrated chemical processing apparatus, include the elimination of many interconnections and joints, thereby reducing the potential for leaks. These and other objects, features and advantages will become better understood upon having reference to the following description of the invention.